The present invention relates to an impact strength modifier capable of imparting both excellent weathering resistance and impact resistance, and to a resin composition comprising the impact strength modifier and a thermoplastic resin, particularly a rigid vinyl chloride resin.
This application is based on a Japanese Patent Application No. Hei 10-198882 filed in Japan, the contents of which are incorporated herein by reference.
Thermoplastic resins, particularly vinyl chloride resins, are widely used resins, but have such drawbacks as poor impact resistance. To improve the impact resistance, various methods have been suggested.
For example, there has been suggested a method of using a mixture prepared by mixing an MBS resin, which is obtained by graft polymerization of a butadiene rubber polymer with methyl methacrylate, styrene or acrylonitrile, with a vinyl chloride resin. However, when using the MBS resin in combination with the vinyl chloride resin, the impact resistance is improved but the weathering resistance is lowered. Therefore, a molded article of the vinyl chloride resin incorporating the MBS resin has such the drawback that the impact resistance is drastically lowered when using it outdoors. It is considered that the weathering resistance is lowered by deterioration of a butadiene unit constituting the MBS resin due to ultraviolet light.
Thus, there has been suggested a method of providing a vinyl chloride resin with both weathering resistance and impact resistances by using, as an impact strength modifier, resins obtained by graft polymerization of a crosslinked alkyl (meth) acrylate rubber polymer comprising an alkyl (meth) acrylate and a crosslinking agent, and methyl methacrylate, styrene or acrylonitrile in Japanese Unexamined Patent Publication, First Publication No. Sho 51-28117. When using such an acrylic graft copolymer as the impact strength modifier, the resulting molded article is superior in weathering resistance and is less susceptible to lowering of the impact resistance. However, there is the problem that a large amount of the acrylic graft copolymer must be added to impart the impact resistance and properties which can provide impact strength, particularly properties which can provide impact strength at low temperatures, are poor as compared with the case of using the MBS resin as the impact strength modifier.
As the another method of improving the impact resistance of the thermoplastic resin, for example, a method of using a multi-layer composite interpolymer having a two-mode distribution, comprising an elastomer inner phase and a rigid non-elastomer outer phase is suggested in Japanese Unexamined Patent Publication, First Publication No. Sho 63-270715 and Japanese Unexamined Patent Publication, First Publication No. Sho 63-270716.
The impact strength modifier further includes, for example, a core/shell type impact strength modifier comprising a core section having rubber elasticity and a shell section made of a rigid thermoplastic resin component, which is suggested in U.S. Pat. No. 3,678,133, and an impact strength modifier obtained by polymerizing a specific alkyl acrylate after subjecting it to a homogenization treatment to prepare a rubber polymer, and polymerizing a vinyl monomer in the presence of the rubber polymer without adding an initiator, which is suggested in Japanese Unexamined Patent Publication, First Publication No. Sho 63-33764.
However, the impact resistance of the resin could not be improved sufficiently even when using any of these impact strength modifiers.
An object of the present invention is to provide an impact strength modifier, which improves the impact resistance, particularly impact resistance at low temperatures, of the resin and satisfactorily maintains the weathering resistance of the resulting molded article by adding a small amount of the impact strength modifier.
The impact strength modifier of the present invention can improve the impact resistance, particularly the impact resistance at low temperatures, of the resin and satisfactorily maintain the weathering resistance of the resin by adding a small amount of the impact strength modifier to the resin. Accordingly, a molded article of a resin composition incorporating this impact strength modifier is superior in impact resistance and also satisfactorily maintains its weathering resistance such as fade resistance or impact resistance. This impact strength modifier is particularly suited for incorporation into a vinyl chloride resin.